1. Field of the Invention
The invention relates to the field of test equipment for aircraft and, in particular, to a support and restraint system for testing a vertical takeoff and landing aircraft during ground testing.
2. Description of Related Art
Fixed wing aircraft with closed loop control systems are subjected to a structural coupling test to insure there is no coupling between the inertia of the control surfaces, and the vehicle management sensors (VMS) that can cause a destructive feedback. The high frequency, 10 Hz, of the control system, generally allows the test to be run with the aircraft on its landing gear, and with the tires slightly deflated, providing a 2 xc2xd to 3 Hz support system. The controls are powered by an external hydraulic system. The stable gear and low power make it an inexpensive and low risk approach. The coupling, that is always found, is easily filtered in the VMS, once identified.
However, on certain vertical takeoff and landing aircraft such a system will not work effectively. The X-35B Joint Strike Fighter proposed by the Lockheed Martin Corporation is unique in the vertical lift flight mode. During this phase the vehicle is supported on a cold thrust post of air in the front of the aircraft (behind the cockpit) and a hot thrust post at the rear of the aircraft using a swiveling nozzle and a pair of under wing thrusters for roll control. The VMS closes the control loops on these effectors in pitch, roll and yaw to provide stable flight. The aircraft""s response to these effectors is expected to come from both inertial feedback of the heavier devices, and pneumatic control force response from low inertia, high thrust effectors. All of these effectors are coupled to the engine through the VMS and the engine full authority digital control (FADC). To explore the structural coupling of the vertical lift system, the propulsion system must be powered. The difficulty of this task is the extra soft support required and the high power settings necessary on the aircraft for testing. The ideal test set up is one that would allow low initial power settings, and be adjustable to handle increasing power settings up to full power settings without requiring major changes in the test setup.
Thus, it is a primary object of the invention to provide a system for ground testing an aircraft to determine potential problems in the flight control system.
It is another primary object of the invention to provide a system for ground testing a vertical takeoff and landing aircraft to determine potential problems in the flight control system that is simple to adjust.
It is a further object of the invention to provide a system for ground testing a vertical takeoff and landing aircraft to determine potential problems in the flight control system that is inexpensive to manufacture.
The invention is a system for supporting a vertical take off and landing aircraft during hover tests about the ground, the aircraft having a longitudinal, vertical, and lateral axis, a nose landing gear and a main landing gear positioned rear therefrom on either side of the longitudinal axis. In detail, the system includes a bearing assembly, preferably an air bearing assembly positionable under the nose and each main landing gear. An air cushion assembly is mounted to each of the air bearings with the air cushion assembly detachably coupled to each landing gear. Preferably, the air cushion assemblies are coupled to the landing gear wheel axles. Thus the bearing assemblies allow horizontal motion above the ground and the air cushions provide for vertical movement of the aircraft above the ground.
A first restraint assembly is coupled between the nose landing gear and the ground positioned along the longitudinal axis, second and third restraint assemblies are coupled between the main landing gear and the ground parallel to the longitudinal axis; third and fourth restraint assemblies are coupled between the main landing gear and the ground extending laterally outward from each side of the aircraft, and fifth and sixth restraint assemblies are coupled between the fuselage aft of cockpit of the aircraft and the ground extending latterly outward from each side of the aircraft; These restraint assemblies bias the aircraft to a centered position.
Preferably each restraint system incorporates a cable assembly that includes a first cable having first and second ends, with the first end attached to the to the aircraft. A second cable is included having first and second ends, with the first end attached to the ground. A spring assembly is attached to and between the second ends of the first and second cables. The spring assembly preferably includes a first wheel assembly coupled to the second end of the first cable and a second wheel assembly coupled to the second end of the second cable. A first tube is attached by its first end to the first wheel assembly. A second tube is attached to the second wheel assembly and the second end is in slidable engagement with the second end of the first tube.
A device to induce sliding resistance between the second ends of the first and second tubes is incorporated. It includes the second end of the second tube having an inwardly tapered threaded end with the tapered end having a plurality of longitudinal grooves forming a plurality of semi-flexible fingers. A rut is threadably engagable with the threaded end of the second end of the second tube. Thus when the nut is treaded onto the second end of the second tube, the plurality of semi-flexible fingers are forced in contact with the second end of the first tube increasing the friction between the first and second tubes.
A biasing spring is coupled between the first and second wheel assemblies for resisting movement of the first and second wheel assemblies apart from each other. Preferably the biasing spring is a plurality bungee cords attached between the first and second wheel assemblies.
The air cushion assemblies include first and second air cushions mounted on the air bearing assemblies in a spaced relationship. A xe2x80x9cTxe2x80x9d shaped structural member having first and second arms and a leg with the leg extending. downward between the first and second arms positioned on top of the first and second air cushions, respectfully. The landing gear wheel axle is mounted to the arm of the T shaped member. A beam, having first and second ends, is attached by its first end to the air bearing assembly, and extends vertically upward from one end of thereof. A positioning arm is pivotally connected to the second end of the beam and also pivotally connected to arm of the T shaped member. Thus the T shaped member is movably mounted to the air bearing assembly.
The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description in connection with the accompanying drawings in which the presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for purposes of illustration and description only and are not intended as a definition of the limits of the invention.